Performances of Fatigue Crack Growth for Aluminum Friction Stir Welds and Base Materials

• Main Authors: QIN Hongshan, YANG Xinqi
• Format: Article
• Language: zho
• Published: Journal of Aeronautical Materials 2017-10-01
• Series: Journal of Aeronautical Materials
• Subjects: Friction stir welds; AA7075-T6 and LC4CS alloy; fatigue crack propagation; fatigue fracture surface
• Online Access: http://jam.biam.ac.cn/CN/Y2017/V37/I5/41

The fatigue crack propagation performances for friction stir welded AA7075-T6 and LC4CS (a Chinese brand aluminum alloy similar to AA7075-T6) joints and their corresponding base materials have been investigated. It was found that the fatigue crack growth rates (d<i>a</i>/d<i>N</i>) for AA7075-T6 welded joints along the weld center line, advanced and retracted side regions are all slower than that of LC4CS alloy, but the d<i>a</i>/d<i>N</i> values along the perpendicular direction of weld for both alloys are the approximate same values. The d<i>a</i>/d<i>N</i> along the weld center line is the lowest, the second is that of retracted and advanced side and the d<i>a</i>/d<i>N</i> along the vertical direction of weld is the highest. The d<i>a</i>/d<i>N</i> of AA7075-T6 FS welds is slower at the range of low load Δ<i>K</i> compared to base material, but for the range of high Δ<i>K</i>, the d<i>a</i>/d<i>N</i> of AA7075-T6 base material is slower. The fracture surface of crack growth along the weld center line is obviously different from that of advanced and retracted side regions and base materials. The typical fatigue striations can be observed across the surface of fatigue crack stable growth for advanced and retracted side regions and base material, but not any fatigue striation can be found along the fatigue fracture surface of weld center line. The resistance of fatigue crack propagation for AA7075-T6 FS welds is better than that of LC4CS welds and the fine and equiaxed grains at nugget region have no good benefit to reduce the d<i>a</i>/d<i>N</i> of AA7075-T6 and LC4CS FS welds.